Automatic selecting switch



Feb. 13, 1951 0. P. LONG AUTOMATIC SELECTING SWITCH 2 Sheets-Sheet 1Filed Oct. 21, 1946 lnvenlor DOUGLAS PERCY LONG Allorney Q Feb. 13, 1951o. P. LONG AUTOMATIC ssuzcnuc swnca 2 Sheets-Sheet 2 Filed Oct. 21, 1946m l. n e n I DOUGLAS PERCY LONG A [tor/nay Patented Feb. 13, 1951 UNITEDSTATES PATENT OFFICE AUTOMATIC SELECTING SWITCH Application October 21,1946, Serial No. 704,639 In Great Britain December 14, 1945 6 Claims. 1

This invention relates to telephone and like selective systems usingautomatic selecting switches. It is particularly applicable to systemsusing single motion selecting switches, commonly referred to asuniselectors. With switches of this type, set in accordance with amarking applied to contacts in its bank, the contacts or outlets of agroup that can be marked may be variable both in number and position.Different methods of obtaining large groups of outlets have beenproposed but the maximum number of contacts which may be traversed by awiper within the period, known in automatic telephone systems as theinter-train pause, is determined by the speed of operation of theselecting switch. This limitation together with that imposed by thepracticable size of the switch determines the number of contacts, andtherefore the number of outlets, that can be provided at any one switch.In a particular known type of uniselector the contact arcs contain 50outlet contacts, this being a suitable number for a switch operating ata speed of traverse of 200 contacts a second, and by a combination ofmethods it has been possible to provide a group selecting switch with200 outlets and to arrange that the wipers in their search for a freeoutlet have not to pass over more than 58 outlet contacts, so that thetime available for searching a group is not exceeded. With such anarrangement, four sets of four wipers and contact arcs have beenprovided, making a total of sixteen wipers and contact arcs, there beingfour wipers for each speaking wire and for each test wire, and fourmarking wipers. The contact arcs may be so arranged that there are fourgroups of fifty outlets, or other grouping may be arranged in which thetotal number of groups multiplied by the number of outlets in each groupdoes not exceed 200.

The present invention has in view arrangements whereby the number ofoutlets that can be had from a selecting switch of a given size andoperatin at a prescribed speed can be increased beyond that hithertoavailable.

In the present invention a selecting switch is provided with a pluralityof wiper sets, each set comprising two line wire wipers and a test orholding wire wiper, a particular one of these sets being adapted to beconnected up in accordance with the number of impulses received at theswitch for the purpose of outlet group selection. There is also amarking wiper common to the several sets of wipers and adapted to beconnected in the test circuit for determining the outlets which are tobe tested. The contacts in the several arcs of the selector are groupedcorrespondingly and the marking of a group in the marking arc ensurestest taking place over contacts situated in like positions in the testwire arcs. If some of the sets of outlet arcs contain only one group ofoutlets while other sets contain more than one group, it must bearranged that the markings for the single group are made in such amanner that no commoning of the groups of contacts in the marking arctakes place except in the case of digital values denoting a sole groupin an outlet arc. The outlet wipers are conveniently connected tocontacts of an impulse responsive device such as a digit switch which,by its response to a train of impulses, connects up a particular set ofwipers. The contacts of the marking arc may be cross-connected so thatin response to impulses denoting a digital value, the contacts markedcorrespond in position to the contacts of the outlets of the groupdenoted by that value in the outlet arcs. Where a set of outlet arcsincludes outlets in more than one group the corresponding wipers wouldbe connected to a like number of contacts in the digit switch anddiiferentiation between the groups would be effected by a like groupingof the contacts in the marking arc and the marking of the several groupsover a further arc of the digit switch. Each outlet group may serve forcalls denoted by a pair of digital values and a discriminating signalmay be passed forward to the succeeding selector for route selectionaccording to the particular digital value that brought about selectionof the outlet. In a similar way the selector itself may be selectable byeither of two digital values and may be adapted to receive adiscriminating signal for the purpose of route selection. This signalmay take effect on a relay a contact of which is adapted in its frontand back positions to mark one or other group of contacts in the markingarc of the selector, the outlets being arranged so that one outlet arcincludes all the outlets of two groups, one group corresponding inposition to contacts in the marking are marked over the relay contact inthe other position.

While a digit switch has been referred to, it will be obvious to thoseskilled in the art that the impulse responsive device may be a relaychain or combination of relays, contacts of which suitably arrangedwould be connected in the circuits of the line and test wires and of themarking wiper. The impulse responsive device may also be used fortransmitting the signal to dinerentiate between the two values of adigit indicative of a selected outlet. The impulse responsive device maybe included in a circuit common to a number of selectors in which casethe selection of the appropriate set of selector wipers may be efiectedby means of relays in the individual selector circuit and operated byand in accordance with the setting of the impulse responsive device.

Arrangements for carrying out the invention will now be described by wayof example with reference to the accompanying drawings which show thecircuits of an incoming selector in an automatic telephone system.

Fig. l of the drawings shows a selector at the incoming end of ajunction that is picked up in response to a single value of a digit, andFig. 2 shows a selector at the incoming end of a junction that is pickedup in response to either of two diiierent values of a digit. Thecircuits of the incoming selector shown in Fig. 1 will first bedescribed aiter which a brief description of the circuits of theselector shown in Fig. 2 will be given with a more de tailed descriptionof those circuits that differ from those shown in Fig. 1. The selectoris a motor driven uniselector, the driving mechanism being designatedgenerally by MU. The selector has 16. wipers and arcs of contacts eacharc containing 52 contacts of which 50 are connected to outlets. Thereare five wipers and corresponding arcs associated with each of the twoline wires and the test and holding wire, and a single marking wiper andcorresponding arc. The selector is adapted to search in a group ofoutlets in response to a single digit which may be of only one value orit may be of either of two values, the position in the selector arcs ofthe of the outlet group to be searched being marked in the marking areby a di it switch which also connects up the appropriate set of wipersin the line and test wire circuits. The digit switch is an eleven pointstepping switch, the switch being of the reverse drive pawl and ratchettype, and the contact arcs in the line and test wire circuits areconnected in pairs to the corresponding wipers of the selector. Theoutlets from the selector may be grouped in five groups of 50 outletseach or ten groups of 25 outlets each or there may be some groups of 50outlets and some of 25 outlets, or other grouping arrangements totalling50 outlets in two groups. In the case of groups of 25 outlets each thecorresponding contacts in the arc of the marking wiper, designated G inthe drawing, are connected to the relevant contacts in the arc of wiperM4 oi the digit switch. A similar connection is made for groups of 50outlets but in this case 25 outlets are connected to the relevantcontact in the arc M4 and the remaining outlets are connected to therelevant contact in the arc of wiper M3. Similar considerations apply toother groupings totalling 50 outlets in two groups. If all the groupscontain 50 outlets each the contacts in the arc of wiper G may beearthed directly. As each wiper of the selector can only extend aconnection over any one of 50 outlets and is connected to a singlecontact or a pair of contacts of the digit switch, each selector arcmust contain contacts of one group of 50 outlets or two complete groupseach of a lesser number of outlets totalling 50. An outlet may, however,be taken into use in response to either of two values of a digit anddiscrimination between its two values may be efiected at the succeedingswitching stage by means of a signal passed forward when the selectorhas switched the connection through. The digit switch, besides the fivewipers referred to, has an oiT-normal wiper Mi, a wiper M2 fordetermining whether a discriminating signal is to be passed forward ornot, and a wiper M8 for the operation of the appropriate overfiow meterif congestion of an outlet group is encountered. The digit switch magnetis designated DM and is provided with a self-drive contact dm. Therelays shown are the impulse receiving relay A, switching control relayB, slow-releasing dialling relay C, high-speed test relay '1' andholding relay H. The selector has off-normal contacts Ni and N2.

When the junction is taken into use, relay A operates by means of itsright-hand winding in a loop over the junction and wiper M2 to earthconnected to the normal contact in the associated contact are. Contacta! closes an operating circuit for relay B over resistance YB and magnetDM but the magnet will not operate in this circuit. Relay 3 on operationholds over its contact bi and at contact 122 extends earth over Wiper Mi at normal to the right-hand winding of relay C. Contact 193 preparesan operating circuit for the driving mechanism MU of the selector,contact b5 prepares an operating circuit for relay I-I, contact b5closes a point in the selector test circuit, contact 12% maintains earthon the positive junction wire after impulsing has commenced, and contactb! connects earth to wiper M3, lighting lamp PG over the normal contactin its contact are and closing a circuit for a delayed alarm relay.Consequent on the operation of relay C, contact cl connects the lowresistance left-hand winding of that relay in the operating circuit formagnet DM which is not closed at this time, contact c2 opens a point inthe initial operating circuit or" the selector driving mechanism MU,contact c3 opens a point in the operating circuit for relay H, andcontact 05. disconnects the arc of contacts of wiper M2- from thepositive junction wire. The magnet DM will not operate in series withrelay B. The impulses received by relay A are repeated to magnet DM inthe following circuit: earth over contact bi, back contact ai contact0!, left-hand winding of relay 0, and contact h? in parallel withresistance YB, magnet DM to battery. Magnet. DM responds to the repeatedimpulses and steps the digit switch accordingly. At the first step ofthe digit switch, the circuit of the delayed alarm relay is opened atwiper M3 and lamp PE is extinguished. When relay A releases, contact aishort-circuits relay B exerting a delaying effect on that relay so thatit does not release during the impulse break period. As soon as relay Are-operates after the first impulse break, the digit switch is steppedfrom its normal position and thereafter relay 0 remains operated by theoperating current of the digit switch magnet during impulse breakperiods and is held by means of its copper slug during the shorterimpulse make periods. At the end of the impulse train, relay A remainssteadily operated and after a brief interval relay 0 releases; Thecircuit of the selector driving mechanism MU is now closed from earthover wiper Ml, contacts b5, 02, t! and hi. The operating right-handwinding of relay H is short-circuited at this time. The selector is setin motion and as soon as its wipers leave their normal position, theoff-normal contacts are operated. Contact Ni maintains the operatingearth for the mechanism- MU and contacts N2 leave relay B dependent onits contact bi. According to the setting of the digit switch by thereceived train of impulses, a particular set of wipers of the selectoris selected by wipers M5, M6 and M1, and the contacts of the marking areassociated with wiper G of the selector are marked over wiper M4 or overwipers M3 and M4. If the outlet group designated is a 25 outlet group,the appropriate contacts in the arc of wiper G are earthed over wiper M4while if the outletgroup contains 50 outlets, 25 of these will be markedover wiper M3. If any other grouping is provided, the marking will bearranged in a similar manner to that described for a group of 50outlets. When the selector wipers reach contacts in the desired group,the test relay T is connected on one side over wiper M1 to the testwiper selected by the digit switch and on the other side over wipers Gand M4 or M3 to earth. When a free outlet is encountered, relay Toperates in the following circuit: earth over wiper M4, or earth overcontact b1 and wiper M3, wiper G, rectifier MRA, both windings of relayT in series, contact b5, wiper M7, the selected test wiper to battery onthe test wire of the outlet. Contact tl opens the operating circuit forthe mechanism MU and switches the high resistance right-hand winding ofrelay H in series with the magnet, and in its front position contact tishort circuits the lower winding of relay T and connects a lowresistance earth to the test wiper to busy the outlet. Relay H operatesin series with mechanism MU but the resistance of the circuit is toohigh for the mechanism to remain operated so that the switch is stopped.Contact hl opens a point in the operating circuit for the mechanism MU,contacts 7L2 and k3 switch through the line wires and open the circuitof relay A, contact 714 connects both windings of relay H in seriesbetween battery over mechanism MU and earth on the test wiper, contacth5 maintains earth over contact 04 on wiper M3 and prepares for theoperation of an over-flow meter if necessary, contact h6 prepares forthe transmission of a busy signal if necessary and contact 71.! opens apoint in the self-drive circuit for magnet DM. Relay A releases,Following on the seizure of the outlet, earth is applied in thesucceeding circuit to the test wire thereby short-circuiting relay T andbringing about its release, and holding relay H independently of relay Bwhich commences to release by reason of its being short-circuited overcontact al on the release of relay A. When re lay B releases, the homingcircuit of the digit switch is prepared at contact b3 and earth isdisconnected from the junction point of the two windings of relay H atcontact b4 and the test relay is disconnected at contact 215. Contact b8disconnects earth from the positive wire if this has been applied aswill be referred to later. At the end of the conversation, release isinitiated by the disconnection of earth from the test and holding wireand relay H is released. Contacts h2 and 723 and 714 disconnect the lineand test wire wipers, contact hl connects earth over contacts Ni and tlto mechanism MU and contact 11.! closes the homing circuit for the digitswitch which self-drives by the operation of its magnet over wiper Ml,contacts b3, dm and it! until the normal position is reached in whichthe circuit is opened at wiper MI. The selector homes by the operationof the mechanism MU in the above described circuit until it reachesnormal where the circuit is opened at contacts NI.

If an outlet is selectable by a pair of values of a digit, adiscriminating signal is sent forward following the operation of relayH. The values of a pair may be and conveniently are an odd value and aneven value. If the value is odd, then, following the operation of relayH, the subsequent impulse-receiving relay will operate round thejunction loop in series with a discriminating relay. If the value iseven, the positive junction wire will be earthed over contact bE, wiperM2 and contact 06, and the said discriminating relay will be shunted andprevented from operating. This earth is subsequently disconnected by therelease of relay B. The operation or non-operation of the discriminatingrelay will bring about an operation such as that described in connectionwith Fig. 2 or a wiper selection or wiper movement for selection in aparticular main group. Arrangements of this latter kind are described inBritish Patent No. 378,585.

If an outlet group is found congested, the selector wipers continue inrotation until the last contacts in the arcs are encountered whereuponthe selector is stopped by the operation of relay T from earth over thelast contact in the arc of wiper G and the relevant test wiper andresistance YC to battery and relay H is operated. Contact h8 connectsearth over the low resistance upper winding of relay T, wiper M1 and thetest wiper in its last contact position, and contact D2 to relay C whichthereupon re-operates. Relay A is connected over the last contacts inthe line wire arcs and resistance YA to a wire that is alternatelyconnected to battery and earth, and a flashing signal is reverted to theout-going exchange. Contacts hi and c5 connect the lefthand winding ofrelay A in a busy tone circuit which is earthed at one end and connectedalternately to battery and earth at its other end but in the oppositephase to that connected to resistance YA so that relay A is held overits two windings alternately. The tone is induced into the line windingof relay A and reverted over the junction. A circuit for the appropriateoverflow meter is closed over contacts bl, n5, c4 and wiper M8. Releasetakes place by the opening of the loop at the outgoing exchange,releasing relay A during a tone period, which is followed by the releaseof relay B and, on the opening of contact b5, by the release of relay H.Relay C is released at contact b2.

If a dead number is called, the selector will not be started. To providefor this, contacts in the arc of wiper M4 relevant to unused numbers areconnected to the normal contact in the arc of wiper G so that relay Twill be operated immediately over a circuit extending from ground overwiper M4, the contact in the arc of wiper M4, wipers M4 and G, bothwindings of relay T, wiper M1, and the normal contact in the arc of theappropriate test wiper to which battery will be con nected. Relay H willbe operated and NU tone will be reverted from a tone circuit connectedto the normal contacts in the arcs of the line wire wipers.

If the selector is held for longer than a prescribed period before thedigit for its setting is received the operation of a relay connected inseries with lamp PG will cause an alarm to be given.

The selector shown in Fig. 2 is connected to a junction seized inresponse to either of a pair of values of a digit, conveniently odd andeven values. The selector is operated in an exactly similar manner tothat shown in Fig. 1 and the following description will be confined tothe circuits and arrangements that differ from those of Fig. 1 due tothe pairing of digital values.

The selector gives access to ten groups of 25 outlets each, each groupbeing selectable by either of a pair of digital values, a discriminatingsignal being passed forward to difierentiate between the two digitalvalues denoting a group of outlets. The contact arc of wiper G of theselector is divided into two parts, 25 contacts in one part beingcommoned and connected to a back contact of a discriminating relay forcontrol of search in an outlet group in respect of seizure of thejunction by an even digital value, and 25 contacts in the other partbeing commoned and connected to a front contact of the discriminatingrelay for control of search in an outlet group in respect of seizure ofthe junction by an odd digital value. The discriminating relay isdesignated P and is adapted to be operated in series with the impulsereceiving relay A at the time the junction is seized unless it isshunted by an earth on the positive wire at the outgoing end of thejunction. The wiper and contact are of the digit switch, designated M4in Fig. l is not required for marking purposes and in Fig. 2 this wiperand wiper M8 are used for the connection of overflow meters. Outletsfrom the selector not in use are connected to a NU tone circuit.

When the junction is taken into use, relay A operates either over thejunction loop and contact 7L3, wiper M2 and the right-hand winding ofrelay to earth or to an earth on the positive wire at the outgoing endof the junction. If the junction is taken into use by the even value ofthe pair of digit values, relay P is not operated due to the shunt overthe positive wire, and earth over contact 312 is connected to the firstcommon set of 25 contacts in the arc of the wiper G. The dialled impulsetrain for the setting of the selector is received by relay A andrepeated to the digit switch in exactly the same manner as thatdescribed for Fig. 1 and at the end of the train search takes place inthe outlet group marked by the digit switch. This group will comprisethe first 25 outlets connected to the arcs of the selector, thecorresponding wipers of which are con: nected up by the digit switch inthe position to which it has been set. The group is selectable by a pairof digital values, the selector wipers being connected to pairs ofadjacent contacts in the arcs of the digit switch. If the received traincomprises an even number of impulses earth will be connected overcontact bi'i, wiper M2 and contact 06 to the positive wire to shunt thediscriminating relay in the succeeding selector. If the received traincomprises an odd number of impulses this earth will not be present andthe discriminating relay in the succeeding selector will be operated inseries with the impulse receiving relay over the junction loop. If astate of congestion is encountered the selector will continue inrotation until the last contact position is reached, whereupon it willbe stopped by the operation of relay T in a circuit from earth on thelast contact in the arc of wiper G to battery over resistance YCconnected to the last contacts in the several test wire arcs, exactly asdescribed for Fig. 1. Relays H and C will be operated and theappropriate overflow meter connected to the arc of wiper M8 will beoperated from earth over contacts bl, 71.5, all and p3. Busy tone andflash signal will be transmitted in the same manner earlier described.

If the junction is taken into use by the odd value of the pair ofdigital values, there will be no earth present on the positive wire atthe outgoing end of the junction and relay P will operate in series withrelay A and will lock up over its left-hand winding contacts pi and b1.Contact p2 will apply the marking earth to the later set of 25 contactscommoned in the arc of wiper G, and search by the selector will takeplace in the outlet group marked by the digit switch. A discriminatingsignal will be passed forward as before described to differentiatebetween the pair of digital values marking the same outlet group. Ifcongestion is encountered busy tone and flash signal will be reverted inthe before-described manner and the appropriate overflow meter will beoperated over the front of contact 103 and wiper M4.

In the event of a spare number being dialled, the selector will bestopped on the first contacts of the group designated by that number,the contact in the relevant test wire are being connected to battery andthe corresponding contacts in the line wire arcs being connected to asource of NU tone which is reverted in the manner earlier described.Although the two groups of a pair have been considered as possessing 25outlets each, it is not necessary that this should be so. The onlyconsideration is that the total outlets in a pair of groups should notexceed 50 and that outlets in each odd or even group correspond innumber.

I claim:

1. In a selecting system, a selecting switch comprising a plurality ofsets of wipers and a marking wiper common to said sets, an arc ofcontacts associated with each of said wipers, each are divided into aplurality of contact sections and each section in the arcs associatedwith said wiper sets having a plurality of outlets connected to thecontacts therein and accessible over the wiper set thereof, each arcsection associated with said marking wiper corresponding to an arcsection associated with each wiper set, selecting means, impulseresponsive means operated upon receipt of a series of impulsesrepresenting a particular digit for operating said selecting means toselect a particular wiper set dependent on the numberof impulses in thereceived series, different digits selecting different wiper sets,marking means also operated by said impulse responsive means to mark thecontacts in one of said contact sections accessible to said markingwiper dependent on the number of impulses in the received series, andmeans effective there after for causing operation of said wiper sets andmarking wiper to thereby cause selection of a particular outlet by theselected wiper set in the section of the contact are corresponding tothe section marked in the banks accessible to the marking wiper.

2. In a selecting system, a plurality of groups of outlets, an automaticselecting switch comprising a plurality of sets of wipers, each sethaving access only to certain of said groups of outlets, marking means,impulse responsive means operated by received series of impulses foroperating said marking means in accordance with a received series ofimpulses representing a particular digit to mark one of the groups ofoutlets accessible to each of said sets of wipers, different groupsbeing marked by different digits, selecting means also operated by saidimpulse responsive means in accordance with said received series ofimpulses representing said particular digit to select one set of wipers,diiferent sets being selected by different digits, and means effectiveafter said wiper set selection for moving the wipers to select onecessible to said selected set of wipers.

3. In a selecting system, a plurality of groups of outlets, an automaticselecting switch com prising a plurality of sets of wipers, each sethaving access only to certain of said groups of outlets, marking means,impulse responsive means operated by received series of impulses foroperating said marking means in one instance in accordance with areceived series of impulses representing a particular digit to mark oneof said groups of outlets accessible to one of said wiper sets and inanother instance in accordance with a diiTerent received series ofimpulses representing a different digit to mark a different one of saidgroups accessible to said one wiper set, different groups being markedby different digits, selecting means also operated by said impulseresponsive means to select said one wiper set in either instance inaccordance with the digit received, and means efiective after saidmarking and selecting for moving the selected wipers to select one ofthe outlets in said one marked group of outlets in said one instance andfor operating the wipers to select one of the outlets in said differentmarked group of outlets in said other instance.

4. In an automatic selector switch, a plurality of wipers comprising aplurality of sets of line wipers and a marking wiper common to saidsets, a plurality of groups of lines accessible from each or" said sets,a plurality of marking contacts accessible to said marking wiper, aselecting device, impulse responsive means operated by received seriesof impulses for operating said selecting device in accordance with aseries of impulses representing a particular digit to select one of saidsets of wipers, different sets being selected by difierent digits, amarking device also operated by said impulse responsive means inaccordance with the same series of impulses to mark one of said markingcontacts, different contacts being marked by different digits, means formovin said plurality of wipers in unison after said selection andmarking, and means responsive to the movement of said marking wiper tosaid marked contact to cause said selected set of Wipers to establish aconnection with a line in one of said marked groups of lines.

5. In an automatic selector switch, a plurality of wiper comprising aplurality of sets of line wipers and a marking wiper common to saidsets, a plurality of groups of lines accessible from each of said sets,a plurality of marking contacts accessible to said marking wiper, aselecting de vice, impulse responsive means operated by received seriesof impulses for operating said selecting device in accordance with oneor another of two difierent series of impulses representing twoparticular digits to select one of said sets of wipers, different setsbeing selected by diiierent pairs of digits, a marking device alsooperated by said impulse responsive means to mark one of said markingcontacts in accordance with the same said one series of impulses in oneinstance and to mark another of said marking contacts in accordance withthe same said other series of impulses in another instance, differentcontacts being marked by diiierent digits, means for moving saidplurality of wipers in unison after said wiper selection and contactmarking, and means responsive to the movement of said marking wiper tosaid one marked contact to cause said selected set of wipers toestablish a connection with a line in one of said groups of linesaccessible from said selected set of wipers in one instance andresponsive to the movement of said marking wiper to said other markedcontact to cause said selected set of wipers to establish a connectionwith a line in another of said groups of lines accessible from saidselected set of wipers in another instance.

6. In a selecting system, a first selecting device comprising aplurality of test wipers and a marking wiper common to said test wipers,a plurality of test contacts accessible to each test wiper, the testcontacts accessible to each test wiper being divided into two groups, aplurality of marking contacts accessible to said marking wiper, themarking contacts being divided into two groups, each marking contactgroup corresponding to a different test contact group accessible to eachtest wiper, a second selecting device comprising a test wiper selectingwiper and a marking contact selecting wiper, impulse responsive meanoperated by received series of impulses for operating said secondselecting device to cause said test wiper selecting wiper to select oneof said test wipers in accordance with either of two different receivedseries of impulses representing two particular digits, different testwipers being selected by either one of two digits in diiferent pairs ofdigits, and to cause said marking contact selecting wiper to select andI mark all of the contacts in one or the other of the two groups ofmarking contacts depending on the particular digit received, each of thetwo groups of marking contacts being selected by different digits insaid pair of digits, and means operated after said test wiper selectionand contact group marking to cause said first selecting means to operateto move said test wipers and said marking wiper in unison to cause saidselected test wiper to select a test contact in the group of testcontacts accessible to said test wiper corresponding to the marked groupof marking contacts.

DOUGLAS PERCY LONG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,762,751 Wright June 10, 19301,900,917 Deakin Mar. 14, 1933 1,914,384 Richardson June 20, 1933 1,92,192 Bellamy Aug. 15, 1933 1,922,237 Escott Aug. 15, 1933 2,272,464Hensler Feb. 10, 1942 2,416,086 Christian Feb. 18, 1947 2,416,109 LongFeb. 18, 1947

